The articulation of the plate oscillating on the housing can be constructed in various ways and, for example, around a ball joint centered at the center of oscillation. However, especially in large and very powerful pumps, the construction of a spherical ball joint articulation capable of withstanding the forces developed is difficult and expensive.
This is why, to simplify the device, it has already been proposed to replace the ball joint by a Cardan joint. Applicants have described in French Pat. No. 2,271,459, an assembly of this type in which the Cardan joint is constituted by a cross-piece pivotally mounted around an axis passing through the center of oscillation and on which the plate is hinged, around a pivoting axis passing also through the center of oscillation and cutting the pivoting axis of the cross-piece at right angles. The plate is provided for this purpose with two spaced portions forming a yoke which caps the cross-piece and on which the ends of an assembly rod directed along the pivoting axis are supported.
Generally, for this type of device, the plate is hinged on the cross-piece around two spaced pivots centered on the pivoting axis and constituted preferably by roller bearings easy to assemble and to maintain. However, such roller bearings run the risk of withstanding such use badly since they are subject to alternate bending stresses on the oscillation of the plate.
This is why, in a second French Pat. No. 79-08735, filed Apr. 6, 1979, applicants have described an arrangement enabling the articulation to be subjected to pre-stressing force directed along the pivoting axis and applied to the assembly rod, for example, by means of a small jack located at the end of the latter and supported on the plate. Preferably conical bearings are used whose external cages are fixed in a cylindrical central housing arranged on the cross-piece in the pivoting axis and whose internal cages take up the pre-stressing force by being supported externally on the two portions of the yoke and internally, on one another, through a spacing ring located between them.
Hitherto, and particularly in French Pat. No. 79-08735, it was sought to space the two roller bearings and the spacing ring as much as possible which had, for this reason, a rather considerable width and tended to buckle. On the other hand, the possible replacement on site of the delicate parts of the mechanism had to be provided for, and particularly the articulation and, consequently, the mounting of the assembly had to be simplified as much as possible.